Rotating double shell heat exchange drum means and method of operating same



July 2, 1957 w. H. FUNK EIAL 2,797,399

ROTATING DOUBLE SHELL HEAT EXCHANGE DRUM MEANS AND METHOD OF OPERATING SAME Filed Dec. 11. 1952 I 2 Sheets-Sheet 1 -5 2o 2 6 46 I I7 I8 2 I I I v INVENTORE WILLIAM H. FUNK GEORGE L. SNYDER ROBERT E. WHITE ATTORNEY July 2, 1957 w. H. FUNK ETAL 2,797,899

ROTATING DOUBLE SHELL HEAT EXCHANGE DRUM MEANS AND METHOD OF OPERATING SAME Filed Dec. 11. 1952 2 Sheets-Sheet 2 INVENTORS $026 56 K m @2308 w m H mo 025%: F s W H. LE

A mum u mo W G R States Patent 2,797,899 Patented July 2, 1957 Ofilice ROTATING DUUBLE SHELL HEAT EXCHANGE lg) MEANS AND METHOD OF OPERATING William H. Funk, Glen Moore, George L. Snyder, Downingtown, and Robert E. White, Havertown, Pen, assignors to Lukens Steel Company, Coatesville, Pa., a corporation of Pennsylvania Application December 11, 1952, Serial No. 325,462

3 Claims. c1. 257-95 This invention relates to an apparatus for cooling or heating which includes a rotary power driven double walled drum means and the method of operating the same. Usually drums are continuously driven at uniform speed and a liquid, such as water, is caused to pass between the cylindrical walls or shells of the drum from one end to the other of the same. Difficulties have been encountered in obtaining a rapid heat exchange between the liquid and the outer shell of the drum due to the fact that when the space or chamber between the inner and outer shells is completely filled with liquid and the drum is rotated, the liquid is carried around with the drum. In such a case, the heat transfer liquid forms a continuous ring between the inner and outer shells of the rotating drum, the said liquid rotating at approximately the speed of the drum. This liquid rotation is due to the drag of the two shells and is also caused by the absence of any hydrostatic head efiect.

An important object of the invention is to provide a method and apparatus for the formation and maintenance of two free liquid surfaces forming a gas pocket between them within the annular space of a double shell heat exchange drum during the rotation thereof, thereby greatly increasing the heat transfer co-efiicient between the heat exchange liquid and the outer shell of the drum.

An additional object of the invention is the method and apparatus for maintaining said gas pocket as stated in the next penultimate paragraph, whereby to continuously or substantially continuously introduce a gas phase within said annular space, and the maintenance of the liquid surface level of said free liquid surfaces, below the top of the inner shell during the rotation of said drum.

A further object of the invention is to provide a method and means for continuously introducing a mixture of heat exchange liquid and a gas entrained therein between the shells of a rotating drum and continuously withdrawing said liquid and gas.

Yet another object of the invention is to provide a method and apparatus for introducing a heat transfer liquid into which a gas has been injected between the shells of a drum and withdrawing the heat transfer liquid and gas, and following the withdrawal of the liquid and gas reconditioning the liquid, i. e., recooling or reheating said liquid, and reintroducing said liqud with fresh or recirculated gas to the space between said drum shells.

Other objects and advantages of the invention will become more apparent during the course of the following description taken in connection with the accompanying drawings.

In the accompanying drawings, forming a part hereof:

Figure l is a central longitudinal vertical sectional view partly broken away and partly in full lines of one form of the apparatus;

Figure 2 is a vertical sectional view of the drum with the pumping spokes shown in dotted lines, taken substantially medially of the drum; and

Figure 3 is a view similar to Figure l, of another form of the invention.

Referring to Figures 1 and 2, the apparatus shown thereby includes a rotary drum 1 consisting of outer and inner shells 2 land 3, respectively. Said shells are connected to each other in any suitable manner so as to rotate in unison and are provided with hubs 4 which rotate in bearings in the supports 5. The drum will be driven by suitable means such as the pulley 24 and belt 25 driven from an electric motor, not shown. The space 6 between the shells is substantially annular, and this space is connected at each end of the drum to the interior of the hubs 4 by hollow spokes 9. These hubs have caps 10 having stuffing boxes and are connected with the inlet and outlet 11 and 12, respectively.

A heat exchange liquid is introduced from a suitable source into the conduit 13. Air or other gas is forced into the conduit 13 through pipe 14 by means of a blower 15 from an inlet pipe 16. In substitution of the pipes 14 and 16, and blower 15, or supplemental thereto, there is provided a venturi 17 having an air inlet pipe 18 and a valve 19. The venturi includes fluid inlet and exit pipes 20 and 21. When the venturi is used, air will be pulled in from the atmosphere through the pipe 18 and discharged with liquid by means of inlet 11 and hub 4 through spokes 9 into space 6 and from this space through spokes 9 at the other end of the drum, into hub 4 through the outlet 12. Both liquid and gas such as air are forced into outlet 12 by the head of pressure from conduit 13. The amount of liquid is so proportioned with the air or other gas in order that the upper level of liquid will be below the top of the inner shell, as shown in Figure 2. This is accomplished by the regulation of the proportional amounts of liquid and gas entering between the shells in any suitable manner as regulating the speed of blower 15, or adjusting the valve 19 or the amount of liquid entering conduit 13, or a combination of these means. During the rotation of the drum, therefore, the upper level of the liquid indicated at 22 is such that there is a gas space or pocket 23 that extends between the upper cylindrical portions of the shells.

In Figure 3 is represented a modification of the apparatus shown in Figure l, in which a closed circuit for both heat exchange liquid and gas is maintained. In this figure, the rotating drum 50 consists of outer and inner connected shells 51 and 52, respectively. The drum is provided with hubs 53 which rotate in bearings in the sup ports 54. The drum may be rotated by any suitable drive means such as pulley 55 and belt 56 from a motor, not shown. The space between the shells is annular and either end of said space is connected to the interior of spokes 58 whose inner ends connect to the interior of the hubs 53. These hubs have caps 59 provided with stufiing boxes that are connected to the inlet and outlet 60 and 61, respectively.

As indicated in Figure 3, liquid from separating tank 62 is withdrawn through conduit 63 to pump 64. Tank 62 is of conventional type having a transparent sight gauge. Such fluid is forced through the heat exchanger unit 66 which functions to heat or cool the liquid, depending on the circumstances. The liquid is forced through the conduit 69, a part of the liquid being bypassed through pipes 70 and '71 which connect the venturi 72 to the conduit 69. The liquid with entrained gas now enters through inlet 60, the hub 5 and after passing through spokes 58 at the right in Figure 3, enters between the annular space 57 between the peripheries of shells 51 and 52. As shown in Figure 2, the liquid only partially fills this space, there being a gas pocket 23 between the inner and outer shells adjacent the top portions thereof. The exhausted liquid and gas finds its way out of the space between the peripheral portions of the shells through the spokes 58 at the left of Figure 3 and into left hub 53, and exits through conduit 61 to the tank 62. As stated above, the liquid is withdrawn from this tank through conduit 63. The gas rising through the liquid, and which collects above the same in the tank, is drawn upwardly through the pipe 73 to the three-way valve 75. This valve may be alternately connected to the pipe 73 or to the atmospheric inlet 74, or a mixture of gas from pipes 73 and 74 may be obtained by proper adjustment of the valve 75. From the valve 75, the gas passes through the short length of pipe 76 to the venturi 72.

It will be understood that air or any other suitable gas may be used, and that the liquid may be of any of the known types of cooling or heating liquids.

In either of the forms shown and described, the heat transfer liquid cannot rotate with the drum and, because of this, the mean velocity difference between the shells and the heat transfer liquid is substantially equal to the peripheral speed of the drum. In the present construction and method, drag forces of the shells on the liquid, when rotating, tend to pull therewith the adjacent layers of heat transfer liquid, but since the overall body of heat transfer liquid cannot move from its relative position, due to the gas pocket, this results in a great deal of turbulence in the body of the heat transfer liquid. Heat transfer drums of the type shown herein yield a heat transfer coefficient between the heat transfer liquid and the shells that is much higher than would be obtained if the liquid were permitted to rotate with the drum as is the case where no air pocket is provided and where the entire space is filled with heat transfer liquid.

The heat transfer coefficient on the inside of the outer shell might be expected to increase ad infinitum With corresponding drum speeds. This is not the case, however, since other factors, such as terminal temperatures, speed, and heat transfer liquid-shell contact areas, must all be taken into account. The vigorous mixing and recirculation existing in the partially complete annulus of heat transfer liquid, insures a relatively uniform temperature around the shell. This is not the case with prior art structures where the entire interior of the space between the shells is filled with the heat transfer liquid, for in such case there would exist temperature variations circumferentially around the outer peripheral surface of the drum. The utilization of the present method, even with an apparatus which includes a manifold type heat transfer liquid feed at both ends of the drum and the continuous feeding of a gas to and from the drum admixed with said liquid, insures the substantial elimination of circumferential temperature variations as well as variations across the outside peripheral surface of the outer shell.

In both forms of the invention, it is preferred that the air or other gas be supplied continuously along with the heat transfer liquid, rather than introducing a fixed quantity of air or gas at one time and entrapping that air for a prolonged period of time. If the air is not supplied continuously, it is impossible to maintain a sufiicient entrapped air pocket for any length of time. This is particularly the case because of the entraining effect of the heat transfer liquid as well as the pumping action of the spokes of the drum. It has been found that the rate of air removal from the drum is a function of the heat transfer liquid flow between the shells of the drum and also of the drum speed. Additionally, the volume of air retained in the drum must increase with increased drum speed if rotation of the heat transfer liquid is to be avoided. These two factors, drum speed and heat transfer liquid rate of flow, normally go together because increased drum speed entails increased duty and thus requires an increased amount of heat transfer liquid. As a net results, the rate of air injection should be proportioned to the rate of heat transfer liquid flow. It will be understood that several methods of air or gas injection may be used as shown in the several figures of the drawings. The air stream before mixture with the heat transfer liquid may be metered and proportioned to the liquid stream.

The venturi-type injector utilizes the heat transfer liquid as the primary fluid and the entrapped ambient air as the secondary fluid. This method has the advantage that over a fairly wide range of rate of flow of the primary fluid the quantity of secondary fluid entrained is proportional to the flow of the primary fluid. The air or other gas which is discharged at the outlet 12 in Figure 1 and outlet 61 of the structure shown in Figure 3 has small bubbles entrained in the heat transfer liquid. If the liquid is not to be used again, such as would be the case in the structure shown in Figure 1, the air then passes from the system with no difiiculty. However, in those cases where the heat exchange liquid is a coolant which is to be recirculated, such as when a refrigerated brine is used as the coolant, the entrained air must be separated and removed from the brine. This can best be accomplished through the use of the separating chamber or tank 62 in which the air is separated from the coolant, as shown in Figure 3 herein.

The above description and drawings disclose several embodiments of the invention as specific language has been employed in describing the several figures. It will nevertheless be understood that no limitations of the scope of the invention is hereby contemplated, and that various alterations and modifications may be made such as would occur to one skilled in the art to which the invention relates.

As shown in both modifications, the inlet means is provided at one end of the drum and the outlet means at the other end. It is to be understood that the inlet and outlet means may be constructed in several different ways, such as by having both at one end of the drum, as shown in U. S. Patent 2,538,985, issued to G. L. Snyder on. January 23, 1951.

Heretofore reference has been made to the maintenance and formation of two liquid free surfaces as shown in Figure 2. This is provided by maintaining the gas in space 23, such functioning to depress the liquid level to such a point that there is formed the two free liquid surfaces 22 separated by a portion of the inner shell 3. Under these conditions, rotation of the liquid with the shells is deterred by a hydrostatic head equal to the height between the liquid surface and the zenith of the inner shell.

As to the rotational speed of the drum, there are many factors which must be considered such as the size of the drum, the thickness, density and moisture content of the material being treated, the ability of the material to respond to treatment, and the temperature of the heat exchange medium. Generally, however, the speed may be varied to provide optimum operating conditions, the only limitation being that speed should be maintained below a point where the drag forces between the shells and the fluid and the centrifugal forces will cause the liquid to be carried around by the drum shells.

In the claims, the term gas is intended to cover atmosphericair as well as other gaseous mixtures.

Having thus described the invention, what is claimed as new, and what is desired to be secured by Letters Patent 1s:

1. A heat exchange drum means comprising a cylindrical drum rotatable. about a horizontal axis and comprising inner and outer substantially uniformly spaced cylindrical shells, aradially disposed wall connecting said shells atfeach end of said drum to provide an annular chamber therebetween, an axially arranged cylindrical hollow hub mounted in each end of said drum, the inner ends of said hubs being closed and the outer ends being open, a plurality of radially disposed hollow spokes at each end of said drum connecting and in .fluid communication with said chamber and the interior of one of said hubs, said hollow spokes and said chamber constituting the sole means of fluid communication between said hubs, an inlet conduit means in fluid communication with the open end of one of said hubs, an outlet conduit means in fluid communication with the open end of the other of said hubs; said inlet conduit means, said one of said hubs, and said spokes at the inlet end of said drum constituting a means for continuously feeding a heat transfer liquid and a gas admixed therewith to said chamber; said feeding means including means for regulating the proportions of said heat transfer liquid and said gas fed to said chamber so as to maintain therein during the rotation of said drum two horizontally spaced heat transfer liquid surfaces separated by a gas filled pocket in the top of said chamber, the gas in said pocket serving to prevent rotation of said heat transfer liquid with said drum.

2. A heat exchange drum means as defined in claim 1, and a separating tank in fluid communication with said outlet conduit means to separate said heat transfer liquid from said gas, a pipe for conveying liquid from said tank back to said inlet conduit means, a second pipe for returning gas from said tank to said inlet conduit means, said feeding means including means in fluid communication with said inlet conduit means to entrain gas from said second pipe in the liquid conveyed from said tank back to said inlet conduit means.

3. A heat exchange drum means as defined in claim 2, and a pump and a means for changing the temperature of said heat transfer liquid in said second pipe.

References Cited in the file of this patent UNITED STATES PATENTS 1,897,613 Jensen -1 Feb. 14, 1933 1,995,011 Qviller Mar. 19, 1935 2,521,215 Haddeland et al Sept. 5, 1950 2,538,985 Snyder Jan. 23, 1951 2,576,036 Ostertag et al. Nov. 20, 1951 2,582,365 Westphal Jan. 15, 1952 2,703,224 Robinson Mar. 1, 1955 

